1. Field of the Invention
The present invention relates to a zone controller for use in a zone controlled conveyor system. More specifically, it relates to a zone controller that facilitates the change of the conveying mode through simple change of setting according to need.
2. Description of Related Art
A conventional roller conveyor system that has a conveying line divided into a plurality of control zones (zones for control), each zone having a zone controller for controlling conveyance is disclosed, for example, in Japanese Laid-open Patent Application No. Hei. 11-199030.
The conventional roller conveyor system is equipped with a motorized roller and “free rollers” both for conveyance, the motorized roller and free rollers connected by belts spanned over them. Each unit has a photoelectric switch for detecting the presence of article and a “motor driver”, i.e., a controller, for controlling operation of the motorized roller.
Each of the zone controllers, connected electrically to others, drives, brakes and stops the rotation of the roller depending on the signal of presence of article of its home zone (i.e., the zone corresponding to the zone controller) and taking into account the signals of presence etc. transmitted from upstream and downstream zones. Such cooperative control by zone controllers achieves the “zero-pressure accumulating control” that enables conveying articles avoiding collision between articles.
So as to achieve an efficient conveyance, it is important for a conveyor line performing zero-pressure accumulating conveyance to convey articles with intervals as short as possible.
On the other hand, for example in the case that examinations of conveyed articles should be carried out at some working location along the conveyor line, it is required to prolong the time intervals between the arrivals of the conveyed articles at the location, so as to adjust the conveying situation of the articles on the line to the operations and the like in the examination.
Such a conveying mode that prolongs the time intervals between the arrivals of the conveyed articles at a particular location, maintaining a predetermined conveying speed, have not been fully devised, though conventional conveyor systems can stop conveyance at particular zone or vary the conveying speed of the whole conveyor line.
In the case that one wishes to prolong the time intervals between the arrivals of articles, one should either prepare zone controllers with different controlling specification or change the conveying modes of zone controllers by using a separately positioned supervisory or superordinate controller and the like.
It has been difficult to suitably adjust the time intervals between the arrivals of articles responding to the work required in the conveyor line, thus requiring a lot of time and expense in constructing systems. Improvement has been desired.
The invention disclosed in this application is proposed in consideration of the above-mentioned situations, aiming to provide a zone controller that facilitates change of the intervals between the conveyed articles.